When describing Hulga (whose given name is Joy), the narrator—channeling Mrs. Hopewell—uses a hyperbole:
All day Joy sat on her neck in a deep chair, reading. Sometimes she went for walks but she didn’t like dogs or cats or birds or flowers or nature or nice young men. She looked at nice young men as if she could smell their stupidity.
The hyperbole here—in which the narrator describes how Hulga “looked at nice young men as if she could smell their stupidity”—captures the way Hulga tends to look down on other people, judging them as less intelligent than she is. The exaggerated language helps readers to understand just how arrogant Hulga is and helps them visualize the judgmental face that she puts on around those she deems inferior. The description of Hugla disliking "dogs or cats or birds or flowers or nature or nice young men" is also an exaggeration, likely due to the fact that the narrator is channeling Mrs. Hopewell's opinions on her daughter in this scene.
It is notable that Hulga has historically ignored the “nice young men” around her but decides to seduce and trust the Bible Salesman. This suggests that Hulga is not as smart or discerning as she thinks she is, as the Bible Salesman turns out to be much more manipulative and untrustworthy than her other potential suitors.